This invention relates to a workpiece transfer apparatus, and more particularly to a workpiece transfer apparatus utilizing a servomotor as a source of drive.
A transfer apparatus utilized to transfer a plurality of workpieces disposed at a predetermined positions on a working or machining line or to transfer workpieces between not working stations is generally requested to have the following performances.
(a) a capability of correctly transferring the workpiece to a predetermined position (positioning performance) PA0 (b) a capability of changing transfer pitch of the workpiece (transfer pitch changing performance) PA0 (c) a capability of minimizing shocks at the time of start and stop and decreasing the transfer time (transfer speed control performance).
To realize these performances it has been the conventional practice to use electric motors having different speeds. With such method of driving, however, since the speed curve of the movement of a transfer bar is predetermined, it is impossible to obtain an optimum speed curve commensurate with the distance of movement and the weight of the workpiece, so that the transfer efficiency is poor and the transfer time cannot be reduced.
It has also been tried to use a special link mechanism so as to make smaller the speeds at the time of starting and stopping the transfer bar than that of during transfer for the purpose of minimizing the effect of the moment of inertia at the time of starting and stopping the transfer bar. Usually, however, since the speed curve resembles a sine curve or a curve similar thereto, the rate of deceleration immediately before stopping the transfer bar is high, so that it is impossible to correctly stop with small shock, only with the link mechanism. For this reason, it has been necessary to use a special braking mechanism for the transfer bar or the driving motor.